Alkylation of organopolysiloxanes using a hydrocarbon aluminum compound



United States Patent ALKYLATION. F ORGANOPQLYSEOXANES" USING A. HYDRQCARBON COMPOU D :H'erb'ert-Jenkner, .Hannover-Wulfel, Germany, assignongto Kali-Chemie A. G., Hannover, Germany No Draw g, Arurlic fia v M y 19 6 SerialNo. 582,344

Claims priority, application-GermanyMay 5, 195!;

2 Claims, (Cl. 2.60448. 2)

- This-invention, relates to orga poly iloxanesa Mar particularly, the invention isaconcer nednwith ;the. a lk'yflation, of suchpolysiloxanes, I

I have discovered that; organopolysiloxanes. can he 'alkylated with,organoraluminumcompounds.. l l h s way, higher molecular weight organop'olysiloxanes may, be

converted tolower. molecular .weight.organopolysiloxanes,

which however, contain, more alkylgroups,

Sui-table starting; materials for my novel .alkylaltion process are organopolysiloxanes of, the. formula RSiO or (,R SiO and mixturesv or copolymers thereof, wherein R .is a monovalent. hydrocarbon radical wherein R1 andR! .are. monovalentzhydr'ocarbbni radicals as defined above. fonR, and wherezxiisa whqlmnumber larger than 2.

In R and R or R groups, the individual members of the group may have the same or different composition. The organo-aluminum compound causes in said reaction a split of the -SiOfi$i-linkage-quite stable in other reactions-whereby AlO bonds are obtained in addition to new Si--C bonds.

In the first stage of the reaction, alkyl aluminum silanolates are formed, which by further alkylation are converted for instance by splitting off Si-O-Si bonds to lower molecular weight organopolysiloxanes containing a higher number of alkyl substituents.

For example, if octamethylcyclotetrasiloxane (x=4) is reacted with an aluminum trialkyl, AlR the reaction proceeds first essentially as follows:

A1R O [Si(CH O] SiR (CH whereby the corresponding alkyl aluminum silanolate is formed. On further addition of octamethylcyclotetrasiloxane to the reaction product of Equation 3, pure aluminum trisilanolate of the formula can be obtained. Like all other aluminum alcoholates, said aluminum silanolates are readily hydrolyzed, whereby, besides Al(OH) siloxanes having the double number of Si atoms per molecule are obtained by condensation of the silanols first formed by the hydrolysis. In this way, organo polysiloxanes having trialkyl silyl end groups are produced from cyclic organo polysiloxanes.

If the reaction of Equation 3 is carried out with an aluminum Ratented Sept. 23, 1958 excess-of AdRgl, a .further'splitting of the Si-QQa-Si bonds ftakeaplace, for. instance according :to' the following equation.

Ac ording; to his; qua ion:.4-,l he ci e l w rmolecular weight organopolysiloxanes,containing-rmoreqallryl groups R are obtained; they may be recovered by distillation, whilst higher molecular weight polysiloxanes containingttheaoriginal 'numberof organic su bstituents R1. (inithisacase methyl) .-are;formed=byhydrolysis ofrthie residual allcylaluminum silanolate.- By varying thevratio of organo p'olysiloxarie:to organo aluminum compound, .Lma yireadily adjust'theeextent-r-to Which'th'e bonds imme-starting: linear, .c'ycl'ie or crosselinlred organopolysiloxanes are.-split: up;v

If organopolysiloxanes of the. formula (RSiQ gl, are .alkylated witlnaorgano: aluminum compounds, thereactions proceed. through the stage of the diorgano-substituted' polysilox-anes; basically-in the same manner as set forth above.

Generally the reaction can be carried. out without solvents and catalysts at-ordinary pressure up to temperatures o.f;a,bout,250 C, Of,cours,e, it is alsopossible i iqr to the. A w r nkage a er ak as for instance A'l halogen linkages in organo .aluminum .hal1des,

.siwhelq gne qnds ar eprod cedinaddi' an: a y

variations. 1

following examples are merely illustrative of the invention and are not to be construed asJimiting-the ;scope t hereof. Applyingthe principle of the 'alleylation of organopolysiloxanes with organo aluminum;lcqin pounds according to the invention, the skilled,in,-t-he will easily be able to react other combinations of "coinpounds of the type involved.

All parts are given by weight.

Example 1 Percent bz up to 93 C b 951l5 C 17 by l1S-150 C 32 b ISO- C 10 by 180-205 C S Residue 2 The total yield was 960 parts. 98 percent of the high molecular weight dimethyl polysiloxane used as starting material had been converted to lower molecular weight ethylmethyl polysiloxanes (or silanols, respectively).

Example 2 465 parts of a mixture of hexamethyl cyclo trisiloxane and octamethyl cyclo tetrasiloxane (b :60 to 70 C.) were heated with a total amount of 240 parts of aluminum triethyl for a period of 7 hours at a temperature of 220-250 C. At the end of the reaction period 84 percent of the aluminum triethyl had reacted, and 6 percent had been thermally decomposed.

The obtained product was then distilled, without hydrolysis. 32 parts were distilled ofi at a pressure of 12 mm. Hg in the temperature range of 50 to 115 C. The residue contained 35 parts of the obtained aluminum silanolate, which represented at room temperature a yellowish readily hydrolyzable resin.

Example 3 I 485 parts of methyl polysiloxane (RSiO prepared from sodium methylsiliconate solution) were dried for 2 hours at 200 C. in vacuo, and subsequently a total of 190' parts of aluminum triethyl, which is a large excess, were added to the dried product with stirring. n heating at 140-160 C., the initially viscous pulpy mass was converted within 35 minutes to a mobile still cloudy liquid. In order to complete the reaction, heat- 20 parts of aluminum triethyl were added dropwise to 36 parts of an unmeltable elastic dimethyl polysiloxane gel at 150 C. on an oilbath. After 30 minutes, the gel was already completely liquefied. Nevertheless, heating at 160 C. was continued for 6 hours. The conversion, calculated on aluminum triethyl, was 85 per 'cent after 6 hours.

The obtained mixture was treated as discribed in Example l and yielded on distillation at 18 mm. Hg the following fractions:

Percent Below 35 C 14 3545 15 6595 24 95-140 47 The aluminium silanolates prepared according to the invention are readily hydrolized with water or with diluted acids such as hydrochloric acid, sulfuric acid, and also by alkaline solutions such as sodium hydroxide; as solvents for the split olf polysiloxanes I may use ethyl ether, benzene, toluene and the like.

Further organo-aluminum compounds which are useful for the purpose of this invention are: aluminum trimethyl, aluminum tripropyl, aluminum trihexyl, aluminum tricyclohexyl, aluminum ethyl halide, aluminum tn'phenyl.

I claim:

1. A method of alkylating methyl polysiloxanes comprising heating a methyl polysiloxane with a tri-monovalent hydrocarbon aluminum compound wherein said hydrocarbon groups are lower aliphatic radicals, at a temperature of about to 250 C. for a time sufficient to attach siloxane groups of said polysiloxane through their oxygen atoms to the aluminum, hydrolyzing the obtained aluminum silanolate, thereby obtaining an at least partially alkylated polysiloxane, extracting said partially alkylated polysiloxane in an organic solvent, and separating said solvent and polysiloxane by distillation.

2. A method of ethylating methyl polysiloxanes comprising heating a methyl polysiloxane with aluminum triethyl at a temperature of about 100 to 250 C. for a time suflicient to attach siloxane groups of said polysiloxane through their oxygen atoms to the aluminum, hydrolyzing the obtained aluminum silanolate, thereby obtaining an at least partially ethylate polysiloxane, extracting said partially ethylated polysiloxane in an or- 'ganic solvent, and separating said solvent and polysiloxane by distillation.

References Cited in the file of this patent UNITED STATES PATENTS 2,645,654 Hyde July 14, 1953 FOREIGN PATENTS 888,852 Germany Sept. 7, 1953 908,019 Germany Apr. 1, 1954 

1. A METHOD OF ALKYLATING METHYL POLYSILOXANES COMPRISING HEATING A METHYL POLYSILOXANE WITH A TRI-MONOVALENT HYDROCARBON ALUMINUM COMPOUND WHEREIN SAID HYDROCARBON GROUPS ARE LOWER ALIPHATIC RADICALS, AT A TEMPERATURE OF ABOUT 100* TO 250*C. FOR A TIME SUFFICIENT TO ATTACH SILOXANE GROUPS OF SAID POLYSILOXANE THROUGH THEIR OXYGEN ATOMS TO THE ALUMINUM, HYDROLYZING THE OBTAINED ALUMINUM SILANOLATE, THEREBY OBTAINING AN AT LEAST PARTIALLY ALKYLATED POLYSILOXANE, EXTRACTING SAID PARTIALLY ALKYLATED POLYSILOXANE IN AN ORGANIC SOLVENT, AND SEPARATING SAID SOLVENT AND POLYSILOXANE BY DISTALLATION. 